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The Cymatoceratidae is a family of Mesozoic and early Cenozoic nautiloid cephalopods and the most abundant of this kind in the Cretaceous. They are characterized by ribbed, generally involute shells of varied form - coiled such that the outer whorl envelops the previous, as with Nautilus, and sutures that are variably sinuous.〔Kummel 1964. Nautiloidea-Nautilida; Treatise on Invertebrate Paleonology Part K; Teichert and Moore (eds), Geological Society of America and University of Kansas press〕 Cymatoceratids first appear in the Middle Jurassic, derived from the Lower Jurassic ''Cenoceras'' (Nautilidae) and extend as far as the Oligocene.〔 ==Taxonomy== Ten cymatoceratid genera are described in the Treatise Part K, 1964.〔 First to appear was the large, tightly involute, rapidly expanding ''Procymatoceras'' from the Middle Jurassic, followed by the Middle and Upper Jurassic ''Cymatonautilus'' which has a wide umbilicus and subquadrate whorl section. ''Procymatoceras'' and ''Cymatonautilus'' are followed by ''Cymatoceras'' and the similar ''Paracymatoceras''. Six genera are restricted to the Cretaceous; ''Eucymatoceras'' and ''Heminautilus'' from the Lower Cretaceous; ''Anglonautilus'' from both the Lower and Upper Cretaceous; ''Deltocymatoceras'', ''Epicymatoceras'',and ''Syrionautilus''. ''Neocymatoceras'' from the Oligocene from the Oligocene is synonymous with ''Cymatoceras''. Of the Cymatoceratidae, ''Cymatoceras'' has the longest temporal range, extending from the Late Jurassic to the Tertiary Oligocene. The only other to cross a period boundary is ''Paracymatoceras'' which lived during both the Late Jurassic and Early Cretaceous. The others are restricted to a simple period, sometimes to a single epoch. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Cymatoceratidae」の詳細全文を読む スポンサード リンク
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